refactor: share the ACP test launcher

2026-07-14 00:18:00 +08:00
parent e481288a3a
commit 0e7d539bbc
11 changed files with 292 additions and 397 deletions
--- a/packages/support/README.md
+++ b/packages/support/README.md
@@ -4,9 +4,9 @@ Packages that exist to serve development, testing, and the examples rather than

 | Package | Role | ctx key |
 |---|---|---|
-| `acp-snapshot/` | ACP snapshot suite kit: subprocess scenario harness + golden normalizers + the `defineAcpSnapshotSuite` factory | (library — imported by example `*.snapshot.ts` suites) |
+| `acp-snapshot/` | ACP test kit: shared subprocess/client launcher + snapshot harness, normalizers, and suite factory | (library — imported by ACP e2e and `*.snapshot.ts` suites) |
 | `invariants/` | Dev-mode event-contract assertions | (listens on `session/*`, `agent/*`) |
 | `llm-replay/` | Record/replay adapter: short-circuits `llm/stream` from a recorded session JSONL (keyless snapshot tests) | (listens on `llm/stream`) |
 | `subagent-mock/` | Scripted `SubagentProvider` for deterministic seam/tool tests | (registers on `ctx.subagents`) |

-`invariants` runs only in dev mode (contract checks, not runtime behavior). `llm-replay` backs the demos and the snapshot test tier under the per-file coverage gate. `acp-snapshot` carries the snapshot tier's harness/normalizer/suite machinery so every example's suite is a scenario table over one shared, gate-covered implementation. `subagent-mock` exercises the real `ctx.subagents` load path without a model or child agent. A package graduates OUT of `support/` into a product group only when it gains documented product consumers.
+`invariants` runs only in dev mode (contract checks, not runtime behavior). `llm-replay` backs the demos and the snapshot test tier under the per-file coverage gate. `acp-snapshot` carries the ACP subprocess/client boundary plus the snapshot harness, normalizers, and suite machinery, so e2e tests share one launcher and every snapshot suite is a scenario table over one gate-covered implementation. `subagent-mock` exercises the real `ctx.subagents` load path without a model or child agent. A package graduates OUT of `support/` into a product group only when it gains documented product consumers.
--- a/packages/support/acp-snapshot/README.md
+++ b/packages/support/acp-snapshot/README.md
@@ -2,8 +2,9 @@

 The ACP snapshot suite kit: the shared machinery behind the keyless snapshot tier (`pnpm run test:snapshot`, [testing policy](../../../docs/testing.md)). An example gets a full snapshot suite from a scenario table plus a fixtures directory; every compare/guard mechanic lives here, under the per-file coverage gate, instead of being copied per example.

-Three layers, importable separately:
+Four layers, importable separately:

+- **`launchAcpTestAgent` (launcher)** — boots an unbuilt ACP agent from a temp cwd, pins tsx to the repo tsconfig, connects the SDK client over a raw-byte stdout tee, collects session updates and stderr, fails closed on unhandled permission requests, and owns graceful or signalled shutdown. Snapshot and ordinary e2e suites share this process boundary; a test supplies only agent paths, cwd, environment overrides, and any permission policy.
 - **`runScenario` (harness)** — boots the real agent bin as a subprocess via tsx (unbuilt, Loader path), drives it over ACP JSON-RPC stdio from a deterministic `input.json` script, tees raw stdout for the golden + purity check, and harvests every persisted session JSONL (parent + subagent children, primary-first) after a graceful stdin-EOF shutdown. Parameterized by `AgentUnderTest` (`binScript`, `configPath`, `tsconfigPath` — absolute paths; the subprocess cwd is a temp dir outside the repo).
 - **Normalizers** — pure functions turning the two captured surfaces into stable text: `normalizeStdout` (JSON-RPC ids → first-seen sequence; UUIDs/cwd → tokens; doubles as the stdout-purity check), `normalizeSessionLog` (times zeroed, `seq` kept), `scrubSystemPrompts` (prompt text → `{{system}}` in every JSONL), and `scrubRequestHeaders` (the remaining header bulk → `{{tools}}`/`{{messagePrefix}}` outside each pin, structure kept — [pinned-header RFC](../../../docs/rfc/implemented/testing/2026-07-06-pin-request-header-content-in-one-scenario.md)).
 - **`defineAcpSnapshotSuite` (factory)** — registers the whole describe/it tree for a scenario table: per-scenario golden + re-persisted-log compares, record/refresh fixture write-back, the per-header-class pin (`system-prompt.golden.md` plus the JSONL's full tool schemas) with its live uniformity guard, and the fixture guard block (no orphan scenario dirs, required files present, exactly one pin per class, every JSONL prompt-scrubbed, non-pinning fixtures fully header-scrubbed). Each scenario directory's `session.jsonl` plus contiguous `session.<n>.jsonl` siblings are the ordered primary/child inventory; the scenario table does not duplicate their count. Must be called at vitest collection time.
@@ -39,4 +40,4 @@ A scenario booting a differently-composed tree sets its own `configPath` (an ove

 The example also ships a `cordis.snapshot.yml` replay overlay next to its `cordis.yml` (the bin swaps them under `DSH_SNAPSHOT=replay` — [single-source replay config RFC](../../../docs/rfc/implemented/testing/2026-07-04-single-source-acp-replay-config.md)); replay fixtures are served by [`dsh-llm-replay`](../llm-replay/README.md), which this package points at via the `DSH_SNAPSHOT_*` env vars it sets on the child. `pnpm run test:snapshot:record` calls the live LLM and rewrites the recorded scenarios' model fixtures; `pnpm run test:snapshot:refresh` stays keyless, runs the replay overlay, and rewrites stdout, comparable session-log goldens, and each pin's Markdown prompt snapshot from the committed model scripts. Fixture roles, record/replay/refresh semantics, and scenario-table fields are documented on `Scenario` and in the [snapshot RFC](../../../docs/rfc/implemented/testing/2026-06-19-acp-snapshot-tests.md).

-Constraints: `suite.ts` imports vitest, so the package is importable only inside a vitest run (the harness and normalizers have no such dependency but ship from the same entry). ACP-specific by design — the harness speaks the SDK's `ClientSideConnection`. Permission round-trips are scriptable: `InputScript.permissionAnswers` is a FIFO queue of option-kind selections (`allow_once`, `reject_once`, …) the client maps to the agent-issued `optionId` at answer time; an absent or exhausted queue answers `cancelled`, and a kind the request never offered rejects the run (the agent is answered `cancelled`, so a tolerant agent cannot absorb the scenario bug). Session config options are scriptable too: the `setConfigOption` step switches a knob over `session/set_config_option`, and `setConfigOptionExpectError` asserts the bridge rejects an unknown id or out-of-vocabulary value (the error frame stays in the transcript).
+Constraints: `suite.ts` imports vitest, so the package entry is importable only inside a vitest run (the launcher, harness, and normalizers have no such dependency but ship from the same entry). ACP-specific by design — the launcher speaks the SDK's `ClientSideConnection`. Permission round-trips are scriptable: `InputScript.permissionAnswers` is a FIFO queue of option-kind selections (`allow_once`, `reject_once`, …) the client maps to the agent-issued `optionId` at answer time; an absent or exhausted queue answers `cancelled`, and a kind the request never offered rejects the run (the agent is answered `cancelled`, so a tolerant agent cannot absorb the scenario bug). Session config options are scriptable too: the `setConfigOption` step switches a knob over `session/set_config_option`, and `setConfigOptionExpectError` asserts the bridge rejects an unknown id or out-of-vocabulary value (the error frame stays in the transcript).
--- a/packages/support/acp-snapshot/package.json
+++ b/packages/support/acp-snapshot/package.json
@@ -1,6 +1,6 @@
 {
  "name": "@deepseek-ai/dsh-acp-snapshot",
-  "description": "ACP snapshot suite kit: real-subprocess scenario harness, golden normalizers, and the suite factory behind the keyless snapshot tier",
+  "description": "ACP test kit: shared subprocess launcher, snapshot scenario harness, golden normalizers, and suite factory",
  "version": "0.0.1",
  "private": true,
  "type": "module",
--- a/packages/support/acp-snapshot/src/harness.ts
+++ b/packages/support/acp-snapshot/src/harness.ts
@@ -16,54 +16,20 @@
 * @module @deepseek-ai/dsh-acp-snapshot/harness
 */

-import { spawn, type ChildProcessWithoutNullStreams } from 'node:child_process'
 import { cp, mkdtemp, readFile, readdir, rm } from 'node:fs/promises'
 import { existsSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { join, delimiter } from 'node:path'
-import { fileURLToPath } from 'node:url'
-import { Readable, Writable } from 'node:stream'
 import {
  ClientSideConnection,
-  ndJsonStream,
  PROTOCOL_VERSION,
-  type Agent as AcpAgent,
-  type Client,
  type RequestPermissionRequest,
  type RequestPermissionResponse,
  type SessionNotification,
 } from '@agentclientprotocol/sdk'
+import { launchAcpTestAgent, type AgentUnderTest, type LaunchedAcpTestAgent } from './launcher.ts'

-// Resolve tsx's ESM loader to an ABSOLUTE path once: the child runs with its
-// cwd in a temp dir OUTSIDE the repo, where a bare `--import tsx` would not
-// resolve from node_modules. import.meta.resolve gives this package's tsx
-// regardless of the child cwd.
-const tsxLoader = fileURLToPath(import.meta.resolve('tsx'))
-
-/**
- * The agent composition a scenario runs against: which bin to boot and which
- * leaf config it loads. All paths are ABSOLUTE — the subprocess cwd is a temp
- * dir outside the repo, so relative resolution would miss; a suite resolves
- * them from its own `import.meta.url`.
- */
-export interface AgentUnderTest {
-  /** The agent bin entry (e.g. `packages/ui/acp-agent/src/bin.ts`), run unbuilt via tsx. */
-  binScript: string
-  /**
-   * The example's live `cordis.yml`. Under `DSH_SNAPSHOT=replay` the bin swaps
-   * it for the sibling `cordis.snapshot.yml` (the keyless replay overlay), so
-   * one path serves both modes.
-   */
-  configPath: string
-  /**
-   * The repo-root tsconfig whose `paths` map resolves the unbuilt workspace
-   * imports. Passed to the child as `TSX_TSCONFIG_PATH`: tsx finds a tsconfig
-   * by searching UP from the child's cwd — a temp dir outside the repo — so
-   * without the explicit pin the dsh-* imports fail before the bin writes a
-   * byte.
-   */
-  tsconfigPath: string
-}
+export type { AgentUnderTest } from './launcher.ts'

 /**
 * One step of a scenario's deterministic input script (`input.json`). The
@@ -194,11 +160,9 @@ export async function runScenario(input: InputScript, opts: RunOptions): Promise
  // Everything past the temp-dir creation runs under a try/finally that always
  // removes both dirs — so a failure in workspace seeding, spawn, or any step
  // never leaks them (the "e2e tests own their resources" rule).
-  let child: ChildProcessWithoutNullStreams | undefined
+  let launched: LaunchedAcpTestAgent | undefined
  let sessionId: string | undefined
  let sessionLogs: HarvestedLog[] = []
-  const rawBuffers: Buffer[] = []
-  const stderrChunks: string[] = []
  try {
    // Seed the workspace if the scenario ships one (a file the agent reads/edits).
    // Copied into the temp cwd so the agent's bash tools see it; the goldens
@@ -207,51 +171,15 @@ export async function runScenario(input: InputScript, opts: RunOptions): Promise
      await cp(opts.workspaceDir, cwd, { recursive: true })
    }
    const env: NodeJS.ProcessEnv = {
-      ...process.env,
-      TSX_TSCONFIG_PATH: opts.agent.tsconfigPath,
      DSH_SNAPSHOT: opts.mode,
      DSH_SNAPSHOT_FILE: opts.fixtureFile,
      DSH_SNAPSHOT_SESSIONS_ROOT: sessionsRoot,
-      DSH_HOME: join(cwd, '.dsh'),
-      DSH_AGENTS_HOME: join(cwd, '.agents'),
      ...opts.overrideFile !== undefined ? { DSH_SNAPSHOT_OVERRIDE: opts.overrideFile } : {},
      ...opts.childFiles !== undefined && opts.childFiles.length > 0
        ? { DSH_SNAPSHOT_CHILD_FILES: opts.childFiles.join(delimiter) }
        : {},
    }

-    child = spawn(
-      process.execPath,
-      ['--import', tsxLoader, opts.agent.binScript, opts.configPath ?? opts.agent.configPath],
-      { cwd, env, stdio: ['pipe', 'pipe', 'pipe'] },
-    )
-
-    child.stderr.setEncoding('utf8')
-    child.stderr.on('data', (c: string) => stderrChunks.push(c))
-
-    // Tee raw stdout: accumulate the bytes for the golden + purity check, and ALSO
-    // feed the same bytes to the SDK client through a passthrough. Buffer the raw
-    // bytes (not per-chunk utf8 strings) and decode once at the end, so a
-    // multibyte sequence split across two 'data' events can't corrupt the golden.
-    const passthrough = new Readable({ read() {} })
-    child.stdout.on('data', (buf: Buffer) => {
-      rawBuffers.push(buf)
-      passthrough.push(buf)
-    })
-    child.stdout.on('end', () => passthrough.push(null))
-
-    const stream = ndJsonStream(
-      Writable.toWeb(child.stdin) as WritableStream<Uint8Array>,
-      Readable.toWeb(passthrough) as ReadableStream<Uint8Array>,
-    )
-    // Watcher so a step can block until the client OBSERVES a particular
-    // session/update — used by promptAndCancel to pin frame order (send cancel
-    // only after the streamed agent_message_chunk has arrived, so those frames
-    // deterministically precede the cancelled prompt response).
-    const updateWaiters: { match: (u: SessionNotification['update']) => boolean; resolve: () => void }[] = []
-    const waitForUpdate = (match: (u: SessionNotification['update']) => boolean): Promise<void> =>
-      new Promise<void>(resolve => updateWaiters.push({ match, resolve }))
-
    // Permission answers are consumed FIFO across the whole run; exhaustion
    // falls back to `cancelled` so approval-free scenarios keep the plain stub.
    const permissionQueue = [...input.permissionAnswers ?? []]
@@ -263,22 +191,11 @@ export async function runScenario(input: InputScript, opts: RunOptions): Promise
    // callback answers `cancelled` (a well-defined path for the agent),
    // captures the error here, and the step loop fails the run on it.
    let scriptError: Error | undefined
-    const makeClient = (_agent: AcpAgent): Client => ({
-      sessionUpdate(params: SessionNotification): Promise<void> {
-        for (let i = updateWaiters.length - 1; i >= 0; i--) {
-          const waiter = updateWaiters[i]
-          // The index is always in-bounds (i only decreases; splice removes at
-          // i, so lower entries stay valid); the guard satisfies
-          // noUncheckedIndexedAccess.
-          /* v8 ignore next 1 -- unreachable in-bounds guard, see above */
-          if (waiter === undefined) continue
-          if (waiter.match(params.update)) {
-            updateWaiters.splice(i, 1)
-            waiter.resolve()
-          }
-        }
-        return Promise.resolve()
-      },
+    launched = launchAcpTestAgent({
+      agent: opts.agent,
+      cwd,
+      ...opts.configPath !== undefined ? { configPath: opts.configPath } : {},
+      env,
      requestPermission(params: RequestPermissionRequest): Promise<RequestPermissionResponse> {
        const answer = permissionQueue.shift()
        if (answer === undefined) return Promise.resolve({ outcome: { outcome: 'cancelled' } })
@@ -296,10 +213,11 @@ export async function runScenario(input: InputScript, opts: RunOptions): Promise
        return Promise.resolve({ outcome: { outcome: 'selected', optionId: option.optionId } })
      },
    })
-    const client = new ClientSideConnection(makeClient, stream)
+    const active = launched
+    const { client } = active

    for (const step of input.steps) {
-      await runStep(client, step, cwd, waitForUpdate, () => sessionId, (id) => { sessionId = id })
+      await runStep(client, step, cwd, match => active.waitForUpdate(match), () => sessionId, (id) => { sessionId = id })
      // A permission exchange happens while a step's request is in flight, so
      // by the time the step settles any script bug it exposed is captured —
      // fail the run HERE, as a harness error, rather than hoping the agent's
@@ -308,26 +226,22 @@ export async function runScenario(input: InputScript, opts: RunOptions): Promise
    }
    // Done driving: close stdin so the server disposes gracefully (flushing
    // persistence) and exits. Then await exit so the harvested log is complete.
-    child.stdin.end()
-    await waitForExit(child)
+    await active.close()
    // Harvest EVERY persisted log (parent + any subagent children) while the
    // temp dirs still exist, ordered primary-first.
    sessionLogs = await harvestSessionLogs(sessionsRoot)
  } finally {
    // Failure-safe teardown: kill a still-running child and drop the temp dirs
    // even if seeding/spawn/a step/harvest threw, so a flaky run never leaks a
-    // process or dir. `child` is undefined only if spawn itself threw.
-    if (child !== undefined && child.exitCode === null && child.signalCode === null) {
-      child.kill('SIGKILL')
-      await waitForExit(child)
-    }
+    // process or dir. `launched` is undefined only if launch itself threw.
+    await launched?.close('SIGKILL')
    await rm(cwd, { recursive: true, force: true })
    await rm(sessionsRoot, { recursive: true, force: true })
  }

  return {
-    rawStdout: Buffer.concat(rawBuffers).toString('utf8'),
-    stderr: stderrChunks.join(''),
+    rawStdout: launched.rawStdout(),
+    stderr: launched.stderr(),
    cwd,
    ...sessionId !== undefined ? { sessionId } : {},
    sessionLogs,
@@ -339,7 +253,7 @@ async function runStep(
  client: ClientSideConnection,
  step: InputStep,
  cwd: string,
-  waitForUpdate: (match: (u: SessionNotification['update']) => boolean) => Promise<void>,
+  waitForUpdate: (match: (u: SessionNotification['update']) => boolean) => Promise<SessionNotification['update']>,
  getSessionId: () => string | undefined,
  setSessionId: (id: string) => void,
 ): Promise<void> {
@@ -433,16 +347,6 @@ async function runStep(
  }
 }

-/** Resolve once the child process exits (any code/signal). */
-function waitForExit(child: ChildProcessWithoutNullStreams): Promise<void> {
-  // Race guard: both call sites run within one synchronous frame of
-  // stdin.end()/kill(), so the exit event cannot have been delivered yet;
-  // kept for any future caller that awaits in between.
-  /* v8 ignore next 1 -- unreachable race guard, see above */
-  if (child.exitCode !== null || child.signalCode !== null) return Promise.resolve()
-  return new Promise<void>(resolve => child.once('exit', () => { resolve() }))
-}
-
 /**
 * Harvest EVERY persisted `.jsonl` session log under a sessions root, parse each
 * header line, and return them ordered primary-first: the top-level session (no
--- a/packages/support/acp-snapshot/src/index.ts
+++ b/packages/support/acp-snapshot/src/index.ts
@@ -1,13 +1,14 @@
 /**
 * ACP snapshot suite kit — the shared machinery behind the keyless snapshot
- * tier (`pnpm run test:snapshot`). Three layers, composable per example:
- * the subprocess scenario harness ({@link runScenario}), the pure golden
- * normalizers ({@link normalizeStdout} / {@link normalizeSessionLog} /
- * {@link scrubRequestHeaders} / {@link scrubSystemPrompts}), and the suite factory
- * ({@link defineAcpSnapshotSuite}) that registers a scenario table as a full
- * describe/it tree. An example's `*.snapshot.ts` supplies only its
- * {@link AgentUnderTest} paths, its snapshots directory, and its
- * {@link Scenario} table.
+ * tier (`pnpm run test:snapshot`). Four layers, composable per example: the
+ * shared subprocess/client launcher ({@link launchAcpTestAgent}), the scripted
+ * scenario harness ({@link runScenario}), the pure golden normalizers
+ * ({@link normalizeStdout} / {@link normalizeSessionLog} /
+ * {@link scrubRequestHeaders} / {@link scrubSystemPrompts}), and the suite
+ * factory ({@link defineAcpSnapshotSuite}) that registers a scenario table as a
+ * full describe/it tree. Ordinary ACP e2e tests can use the launcher directly;
+ * an example's `*.snapshot.ts` supplies only its {@link AgentUnderTest} paths,
+ * snapshots directory, and {@link Scenario} table.
 *
 * NOTE: ./suite.ts imports vitest, so this package is importable only inside a
 * vitest run — a support-tier constraint stated in the README.
@@ -17,7 +18,6 @@

 export {
  runScenario,
-  type AgentUnderTest,
  type HarvestedLog,
  type InputScript,
  type InputStep,
@@ -25,6 +25,12 @@ export {
  type RunOptions,
  type RunResult,
 } from './harness.ts'
+export {
+  launchAcpTestAgent,
+  type AcpTestLaunchOptions,
+  type AgentUnderTest,
+  type LaunchedAcpTestAgent,
+} from './launcher.ts'
 export {
  normalizeSessionLog,
  normalizeStdout,
--- a/packages/support/acp-snapshot/src/launcher.ts
+++ b/packages/support/acp-snapshot/src/launcher.ts
@@ -0,0 +1,152 @@
+/**
+ * Shared launcher for ACP tests that drive an unbuilt agent subprocess over
+ * JSON-RPC stdio. It owns the tsx loader, workspace-resolution environment,
+ * stdout tee, SDK client, update collection, permission fallback, and process
+ * shutdown so e2e and snapshot suites do not each reconstruct that boundary.
+ *
+ * @module @deepseek-ai/dsh-acp-snapshot/launcher
+ */
+
+import { spawn, type ChildProcessWithoutNullStreams } from 'node:child_process'
+import { join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { Readable, Writable } from 'node:stream'
+import {
+  ClientSideConnection,
+  ndJsonStream,
+  type Agent as AcpAgent,
+  type Client,
+  type RequestPermissionRequest,
+  type RequestPermissionResponse,
+  type SessionNotification,
+} from '@agentclientprotocol/sdk'
+
+// The child runs from a temp directory outside the repo, where a bare
+// `--import tsx` cannot resolve. Resolve this package's loader once instead.
+const tsxLoader = fileURLToPath(import.meta.resolve('tsx'))
+
+/** The unbuilt agent entry, leaf config, and workspace tsconfig an ACP test boots. */
+export interface AgentUnderTest {
+  /** The agent bin entry (for example `packages/ui/acp-agent/src/bin.ts`). */
+  binScript: string
+  /** The leaf `cordis.yml` loaded by the bin. */
+  configPath: string
+  /** The repo tsconfig whose paths resolve unbuilt workspace imports. */
+  tsconfigPath: string
+}
+
+/** Options for one ACP test subprocess. */
+export interface AcpTestLaunchOptions {
+  /** The agent composition to boot. */
+  agent: AgentUnderTest
+  /** Process cwd and default session-home root. */
+  cwd: string
+  /** Alternate leaf config for this launch. */
+  configPath?: string
+  /** Extra environment values layered over the parent environment. */
+  env?: NodeJS.ProcessEnv
+  /** Permission handler; omitted requests fail closed as `cancelled`. */
+  requestPermission?: (params: RequestPermissionRequest) => Promise<RequestPermissionResponse>
+}
+
+/** A running ACP test process and its captured client-side surfaces. */
+export interface LaunchedAcpTestAgent {
+  /** The child process, exposed for process-level assertions. */
+  child: ChildProcessWithoutNullStreams
+  /** The SDK connection backed by the child's stdio. */
+  client: ClientSideConnection
+  /** Session updates in receive order. */
+  updates: SessionNotification['update'][]
+  /** Decode all stdout bytes captured so far. */
+  rawStdout(): string
+  /** Decode all stderr chunks captured so far. */
+  stderr(): string
+  /** Resolve when a future session update matches the predicate. */
+  waitForUpdate(match: (update: SessionNotification['update']) => boolean): Promise<SessionNotification['update']>
+  /** Gracefully close stdin, or send a signal, and wait for process exit. */
+  close(signal?: NodeJS.Signals): Promise<void>
+}
+
+/**
+ * Boot an ACP agent subprocess and connect an SDK client to its stdio.
+ *
+ * @param options Agent paths, cwd, environment, and optional permission handler.
+ * @returns The running process, connected client, captures, and shutdown handle.
+ */
+export function launchAcpTestAgent(options: AcpTestLaunchOptions): LaunchedAcpTestAgent {
+  const { agent, cwd } = options
+  const child = spawn(
+    process.execPath,
+    ['--import', tsxLoader, agent.binScript, options.configPath ?? agent.configPath],
+    {
+      cwd,
+      env: {
+        ...process.env,
+        ...options.env,
+        TSX_TSCONFIG_PATH: agent.tsconfigPath,
+        DSH_HOME: join(cwd, '.dsh'),
+        DSH_AGENTS_HOME: join(cwd, '.agents'),
+      },
+      stdio: ['pipe', 'pipe', 'pipe'],
+    },
+  )
+
+  const stderrChunks: string[] = []
+  child.stderr.setEncoding('utf8')
+  child.stderr.on('data', (chunk: string) => stderrChunks.push(chunk))
+
+  const rawBuffers: Buffer[] = []
+  const passthrough = new Readable({ read() {} })
+  child.stdout.on('data', (buffer: Buffer) => {
+    rawBuffers.push(buffer)
+    passthrough.push(buffer)
+  })
+  child.stdout.on('end', () => passthrough.push(null))
+
+  const updates: SessionNotification['update'][] = []
+  const updateWaiters: {
+    match: (update: SessionNotification['update']) => boolean
+    resolve: (update: SessionNotification['update']) => void
+  }[] = []
+  const stream = ndJsonStream(
+    Writable.toWeb(child.stdin) as WritableStream<Uint8Array>,
+    Readable.toWeb(passthrough) as ReadableStream<Uint8Array>,
+  )
+  const makeClient = (_agent: AcpAgent): Client => ({
+    sessionUpdate(params: SessionNotification): Promise<void> {
+      updates.push(params.update)
+      for (let index = updateWaiters.length - 1; index >= 0; index--) {
+        const waiter = updateWaiters[index]
+        /* v8 ignore next 1 -- index is bounded by the array length */
+        if (waiter === undefined) continue
+        if (!waiter.match(params.update)) continue
+        updateWaiters.splice(index, 1)
+        waiter.resolve(params.update)
+      }
+      return Promise.resolve()
+    },
+    requestPermission: options.requestPermission
+      ?? (() => Promise.resolve({ outcome: { outcome: 'cancelled' } })),
+  })
+  const client = new ClientSideConnection(makeClient, stream)
+
+  return {
+    child,
+    client,
+    updates,
+    rawStdout: () => Buffer.concat(rawBuffers).toString('utf8'),
+    stderr: () => stderrChunks.join(''),
+    waitForUpdate: match => new Promise(resolve => updateWaiters.push({ match, resolve })),
+    async close(signal?: NodeJS.Signals): Promise<void> {
+      if (child.exitCode !== null || child.signalCode !== null) return
+      if (signal === undefined) child.stdin.end()
+      else child.kill(signal)
+      await waitForExit(child)
+    },
+  }
+}
+
+/** Resolve once a running child exits. */
+function waitForExit(child: ChildProcessWithoutNullStreams): Promise<void> {
+  return new Promise<void>(resolve => child.once('exit', () => { resolve() }))
+}
--- a/packages/support/acp-snapshot/tests/harness.spec.ts
+++ b/packages/support/acp-snapshot/tests/harness.spec.ts
@@ -3,7 +3,9 @@ import { tmpdir } from 'node:os'
 import { delimiter, join } from 'node:path'
 import { fileURLToPath } from 'node:url'
 import { afterAll, describe, expect, it } from 'vitest'
+import { PROTOCOL_VERSION } from '@agentclientprotocol/sdk'
 import { runScenario, type AgentUnderTest, type InputStep } from '../src/harness.ts'
+import { launchAcpTestAgent } from '../src/launcher.ts'

 /**
 * Unit tests for the subprocess harness, driven through the REAL spawn path
@@ -38,6 +40,37 @@ async function scenario(behavior: object): Promise<{ dir: string; fixtureFile: s
 const boot: InputStep[] = [{ op: 'initialize' }, { op: 'newSession' }]

 describe('runScenario', () => {
+  it('centralizes ACP boot, captures, updates, fail-closed permissions, and shutdown', { timeout: 20_000 }, async () => {
+    const { dir, fixtureFile } = await scenario({ permissionProbe: true, echoEnv: true, stderrNote: 'launcher stderr' })
+    const sessionsRoot = await mkdtemp(join(tmpdir(), 'acp-launcher-sessions-'))
+    tempDirs.push(sessionsRoot)
+    const launched = launchAcpTestAgent({
+      agent: AGENT,
+      cwd: dir,
+      configPath: AGENT.configPath,
+      env: {
+        DSH_SNAPSHOT: 'replay',
+        DSH_SNAPSHOT_FILE: fixtureFile,
+        DSH_SNAPSHOT_SESSIONS_ROOT: sessionsRoot,
+      },
+    })
+    await launched.client.initialize({ protocolVersion: PROTOCOL_VERSION, clientCapabilities: {} })
+    const { sessionId } = await launched.client.newSession({ cwd: dir, mcpServers: [] })
+    const nextChunk = launched.waitForUpdate(update => update.sessionUpdate === 'agent_message_chunk')
+    await launched.client.prompt({ sessionId, prompt: [{ type: 'text', text: 'go' }] })
+    expect((await nextChunk).sessionUpdate).toBe('agent_message_chunk')
+    expect(launched.updates.some(update => update.sessionUpdate === 'agent_message_chunk')).toBe(true)
+    expect(launched.rawStdout()).toContain('permission:{\\"outcome\\":\\"cancelled\\"}')
+    expect(launched.stderr()).toContain('launcher stderr')
+    await launched.close()
+    await launched.close('SIGKILL')
+
+    // The minimal shape needs no environment or config override.
+    const minimal = launchAcpTestAgent({ agent: AGENT, cwd: dir })
+    await minimal.client.initialize({ protocolVersion: PROTOCOL_VERSION, clientCapabilities: {} })
+    await minimal.close()
+  })
+
  it('drives a full turn: initialize (terminal caps), session, prompt, permission stub, harvest', { timeout: 20_000 }, async () => {
    const { fixtureFile } = await scenario({
      permissionProbe: true,